I was about the same size you were in high school, so I know how it goes. Managed to get down to around 175 at 21, then put it all (plus) back on over the years.

Once you get a food and exercise plan that works for you you'll be amazed at how fast the weight will come off. Good for you that you're doing it now, while you're young--it gets tougher with age!

There's plenty of great people here to lend support. You might check out one of the 100 + to Lose threads (one in Diet Tips and one in the Women's forum). We're also doing a Lose 10% of your body weight challenge by the 4th of July over in Diet Tips if you're interested.